1. Technical Field
The present invention relates to a conjugate fiber comprising a polyester polymer and an olefin polymer, and more particularly, the present invention relates to a conjugate fiber having both the proper amount of heat shrinkage and hot-melt adhesive properties, and a drawn intermediate in which a fine conjugate fiber can be obtained therefrom with high productivity, and an ultrafine conjugate fiber having high strength and excellent thermal stability.
2. Background Art
Olefin fibers such as polyethylene and polypropylene are widely used for hygiene products, filters, etc., because they are safe with respect to the skin, have a small environmental burden, excellent chemical resistance, and the like. On the other hand, polyester fibers such as polyethylene terephthalate and the like are widely used for clothing, industrial materials, etc., because they have high heat resistance, pleat retention properties, and the like. Moreover, the need has arisen to make single yarn increasingly finer to enhance the softness of the texture, softness of the fabric, draping properties, and the like even more.
Generally, method such as spinning ultrafine, undrawn yarn, drawing at a high magnification, and the like have been adopted to reduce the fineness. However, attempting to spin ultrafine, undrawn yarn can bring about a decline in productivity associated with a decrease in the discharge amount, or a decrease in both runnability and productivity associated with an increase in the number of fiber breakage events caused by a high spinning speed, adopted for producing said fiber. Attempting to draw at a high magnification can result in fiber breakage if the magnification is too high, and the fineness of the drawn yarn obtained thereby is self-limiting.
Concerning ultrafine yarn, it has been proposed that drawing an undrawn polyester yarn at a high drawing magnification is possible by drawing at a temperature higher than the glass transition temperature thereof, and that an ultrafine polyester fiber can be obtained thereby (see Patent Reference 1). This involves creating a flow-drawing state by performing a first stage drawing treatment at a high temperature and forming fine fibers while restricting fiber structure development, and then forming even finer fibers while developing the fiber structure in a second stage drawing treatment. There are problems with this method, however, because when attempting to restrict fiber structure development enough for it to be drawn in the second stage, it is necessary to increase the drawing temperature in the first stage and perform drawing at low tension. This can invite instability in the process because the fiber yarn can droop under its own weight as a result of the low tension, and fiber breakage due to drawing can occur because the tension fluctuates greatly in response to fluctuations in drawing temperature. Thus, stable operation and uniform fiber properties cannot be obtained thereby. Furthermore, it has been found that when such a method is applied to polyolefin fibers, the undrawn yarn comprising the olefin material has been crystallized, or tends to crystallize during the drawing process, and because the molecular chains are bent to the extreme, a flow-drawing state cannot be reached therewith. Thus, this has hampered efforts to apply the above drawing method industrially to fibers containing olefin polymer resin material, and exploring that avenue has received no attention.
Another proposal involves creating a uniform flow-thawing state with high-speed in substantial polyester fibers and nylon fibers by heating rapidly with irradiation of infrared rays (see Patent Reference 2). There is a problem with that method, however, because the irradiated area is restricted when heating is performed with a beam of infrared light, and that results in low productivity since many fiber yarn lines cannot be heated all at a time.
[Patent Reference 1] Japanese Patent Application Laid-open No. H11-21737
[Patent Reference 2] Japanese Patent Application Laid-open No. 2002-115117